Genetically engineered bacteria can now produce long-chain alcohols that could be used as biofuel, scientists report in the Proceedings of the National Academy of Sciences [subscription required]. Remarkably, the researchers synthetically modified the bacteria's metabolism to churn out a type of energy-rich alcohol not normally found in nature.
“Previous metabolic engineering work typically produces compounds that already exist in nature,” says coauthor James Liao... “Our work here aims to produce compounds that are not synthesized in nature” [Science News].
In addition to ordinary genetic engineering, which involves taking genes from different species (in this case, genes from yeast and a cheese-making bacteria), the new study also required a third, custom-made artificial gene. The three genes were inserted into the genome of E. coli bacteria. The researchers designed the genes to extend E. coli's
metabolic pathway so that toward the end, the precursor compounds that would normally get converted into amino acids instead turn into long-chain alcohols [Technology Review]. These long-chain alcohols string together six carbon atoms, packing in more potential energy per molecule. Ethanol has only two carbon atoms, and no other naturally-occurring alcohol contains more than five.
Their energy density makes the long-chain alcohols valuable as biofuels: The higher number of carbon atoms gives the biofuels as much energy per gallon as gasoline; by comparison, ethanol has 30 percent less energy than gasoline [Technology Review]. Unlike ethanol, the new biofuel could also be used with existing gasoline infrastructure because the larger molecules are easily separated from water. Although similar large molecule alcohols can be made via artificial processes, those require extreme heat and pressure while the "bacteria factory" operates at body temperature.
Currently, the researchers have managed to produce only a small amount of the alcohol: less than 400 milligrams of fuel output from 20 grams of glucose fed to the bacteria.
"The next step is to develop it in large enough compound quantities and then hand it over to a company for development," said Liao [AFP]. Another obstacle to overcome is the toxicity of the alcohol to the bacteria, but Liao think it's possible to make the bacteria more alcohol tolerant. If they succeed, commented bioengineer James Collins, “You just basically feed the bacteria and keep them happy and they chug along and do all the biochemistry" [Science News].
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